There are 10 athletes at a track meet. How many different ways can they finish first or second?

 90 different ways

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Explanation:

We have 10 ways to pick the first place finisher, and then 10-1 = 9 ways to pick the runner in second. Therefore, 10*9 = 90 different ways.

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The longer method you can use is to apply the nPr permutation formula which is

where in this case, n = 10 and r = 2. The exclamation marks indicate factorial. A permutation is used since order matters.

a² + b²= c²

24² + 7² = c²

c= 25